Protection Induced by Protein-Lipopolysaccharide Complexes in Tobacco Leaves: Role of Protected Tissue Free-space Solutes*

Hypersensitive confluent necrosis in tobacco leaves, caused by Pseudomonas syringae pv. aptata, is prevented by an intercellular injection of protein-lipopolysaccharide (pr-LPS) complexes 48 h earlier. An increase (48 %) in the peroxidase activity and a new low molecular weight protein (ε 17.5 kD) were found in the intercellular fluid of protected tissue (treated fluid) 48 h after pr-LPS infiltration. Up to 24 h after pr-LPS infiltration the treated fluid did not inhibit the in vitro growth of heterologous bacteria. Injected into tobacco leaves 30 min before the bacteria, the treated fluid retarded the rate of intercellular bacterial growth between 8 and 12 h after infiltration of the bacteria compared with the control fluid. Up to 4 h after injection, the attachment of live and dead bacteria to the cell walls occurred in both the protected tissue and in the control; 4 h after injection, however, the dead bacteria were only weakly attached in the protected tissue. Within 20 min after the intercellular infiltration, there was a decrease in the heterologous bacterial number in the protected tissue, 33 % less than that in the control tissue. Protected tissue free-space solutes did not have a direct antibacterial effect but activated an antibacterial response in the leaf tissue. Attachment of bacteria to the cell walls did not in itself trigger hypersensitive confluent necrosis. The protected tissue was initially more favourable for the survival of heterologous bacteria.     

Effect of nitrate,ammonia and nitrogen starvation on the regulation of nitrate reductase in Cyanidium caldarium

Summary Cells of Cyanidium caldarium grown with ammonia or ammonium nitrate as nitrogen source do not contain appreciable nitrate reductase activity. The alga develops the capacity to synthesize the enzyme when it is transferred from the ammonium medium to a nitrogen-free medium. Nitrate is not needed as an inducer and no enhancement in the rate of enzyme synthesis is observed when it is present. By contrast, whereas the synthesis of the enzyme in nitrogen-free medium proceeds at an increasing rate, in the nitrate medium it attains a stationary level after a short time.Nitrate grown cells possess variable amount of inactive nitrate reductase (from 9 to 60%) whereas in nitrogen-free medium the enzyme occurs principally in a fully active form. Addition of ammonia inactivates reversibly the preexisting enzyme. The inactive enzyme is measurable in the crude extract after activation by heating.It is suggested that in Cyanidium the inactivating effect of ammonia, which is the end product of nitrate reduction, in association with the repression of enzyme controls the level of nitrate reductase activity.     

ON THE DIFFERENTIAL RESPONSE OF SARCOPLASM AND MYOPLASM TO DENERVATION IN FROG MUSCLE

Electron microscopic evidence is presented that the early response to denervation ("simple atrophy") of the semitendinosus m. of the frog is characterized by a greater prominence of the sarcoplasmic reticulum and by the presence, in the interfibrillar spaces, of mitochondria which are more numerous and smaller than in normal muscle. In contrast with the dynamic changes of the sarcoplasmic structural components, the myofibrils showed a progressive decrease in diameter after denervation and throughout the period studied. By carrying out tissue fractionation experiments, the yield of microsome-protein was found significantly greater in the denervated muscles, as compared with the contralateral controls, in this initial stage. Under the conditions attending the overdevelopment of the sarcoplasmic reticulum (SR), denervated semitendinosus m. incorporated valine-C¹⁴ into proteins more actively than the control pairs. The denervated muscles also showed an increase in the number of freely scattered and membrane-bound ribosomes and of polyribosomes, suggesting a more active synthesis of the SR membranes. Pronounced atrophy of the myofibrils, disorganization of the SR, and an increased number of ribonucleoprotein particles lying in the enlarged interfibrillar spaces were the main ultrastructural features of "degenerative atrophy" in frog muscle in the late periods after denervation. The probably adaptive character of the early changes occurring on denervation of frog muscle is discussed.     

Destabilizing the AXH Tetramer by Mutations: Mechanisms and Potential Antiaggregation Strategies

The AXH domain of protein Ataxin 1 is thought to play a key role in the misfolding and aggregation pathway responsible for Spinocerebellar ataxia 1. For this reason, a molecular level understanding of AXH oligomerization pathway is crucial to elucidate the aggregation mechanism, which is thought to trigger the disease. This study employs classical and enhanced molecular dynamics to identify the structural and energetic basis of AXH tetramer stability. Results of this work elucidate molecular mechanisms behind the destabilizing effect of protein mutations, which consequently affect the AXH tetramer assembly. Moreover, results of the study draw attention for the first time, to our knowledge, to the R638 protein residue, which is shown to play a key role in AXH tetramer stability. Therefore, R638 might be also implicated in the AXH oligomerization pathway and stands out as a target for future experimental studies focused on self-association mechanisms and fibril formation of full-length ATX1.     

Malaria and HIV: a silent alliance

HIV and malaria are leading causes of morbidity in sub-Saharan Africa. Recently, Abu-Raddad and colleagues explored the synergy between these diseases through a mathematical model that included all documented interactions. It emerges from the model parameter inputs that concomitant infection of both HIV and malaria fuels the spread of both diseases. For the first time, it is shown that, according to the model, transient but repeatedly elevated HIV viral loads due to recurrent co-infections, such as malaria, can also influence and increase HIV prevalence. Probably, these results are conservative and the true impact of the interaction could be even more important.     

Bioengineering thermodynamics of biological cells

Background

Cells are open complex thermodynamic systems. They can be also regarded as complex engines that execute a series of chemical reactions. Energy transformations, thermo-electro-chemical processes and transports phenomena can occur across the cells membranes. Moreover, cells can also actively modify their behaviours in relation to changes in their environment.

Methods

Different thermo-electro-biochemical behaviours occur between health and disease states. But, all the living systems waste heat, which is no more than the result of their internal irreversibility. This heat is dissipated into the environment. But, this wasted heat represent also a sort of information, which outflows from the cell toward its environment, completely accessible to any observer.

Results

The analysis of irreversibility related to this wasted heat can represent a new approach to study the behaviour of the cells themselves and to control their behaviours. So, this approach allows us to consider the living systems as black boxes and analyze only the inflows and outflows and their changes in relation to the modification of the environment. Therefore, information on the systems can be obtained by analyzing the changes in the cell heat wasted in relation to external perturbations.

Conclusions

The bioengineering thermodynamics bases are summarized and used to analyse possible controls of the calls behaviours based on the control of the ions fluxes across the cells membranes.

     

Quercetin can act either as an inhibitor or an inducer of the mitochondrial permeability transition pore: A demonstration of the ambivalent redox character of polyphenols

The Ca²⁺- and oxidative stress-induced mitochondrial permeability transition (MPT) plays an important role in phenomena ranging from tissue damage upon infarction to muscle wasting in some forms of dystrophy. The process is due to the activation of a large pore in the inner mitochondrial membrane. Anti-oxidants are considered a preventive and remedial tool, and mitochondria-targeted redox-active compounds have been developed. Plant polyphenols are generally considered as anti-oxidants, and thus candidates to the role of mitochondria-protecting agents. In patch-clamp experiments, easily oxidizable polyphenols induced closure of the MPT channel. In swelling experiments with suspensions of mitochondria, high (20–50 μM) concentrations of quercetin, the most efficient inhibitor, promoted instead the onset of the MPT. Chelators of Fe^2+/3+ and Cu^+/2+ ions counteracted this effect. Fluorescent indicators of superoxide production confirmed that quercetin potentiates O₂^? generation by isolated mitochondria and cultured cells. Since this was not affected by chelating Fe and Cu ions, the MPT-inducing effect can be ascribed to a “secondary”, metal ion-catalyzed production of ROS. These results are a direct demonstration of the ambivalent redox character of polyphenols. Their mode of action in vivo cannot be taken for granted, but needs to be experimentally verified.